I am assuming you are on Oreo since you mention notifications shifting in order
From Android 8.0 Oreo, thoroughly reviewed
Notifications are ordered on the concept of attention based sorting, as pictorially shown
To quote relevant sections
The panel and notification ordering logic has been refined into a tiered top-to-bottom system. First, there's "Major Ongoing" notifications for things like currently playing music, phone calls, timers, Google Maps navigation, and other running, foreground services. Below that are "People-to-People" notifications, which are incoming text messages and missed calls from various apps. After that are "General" notifications for e-mails, reminders, calendar appointments, and all other apps.
P2P notifications also get to be bigger in Oreo
The new bottom section, which Google has given the perfectly fitting name of "By the Way," houses single-line, minimized-by-default notifications that don't create a status bar icon....The idea is that this section can house notifications that you don't need to deal with right now but might be useful information for you to have...
This explains why you noticed this shifting more when your GPS was on (presumably navigating and this takes high priority